The present invention relates to a stepping motor for driving a head carriage and a disk drive unit comprising such a motor, and particularly to a stepping motor having a lead screw on a motor axis, and a disk drive unit comprising such a motor.
Recently, efforts have been made toward downscaling an equipment comprising a disk drive unit as a storage device, facilitating a strong requirement for downscaling of a disk drive unit that is included in such an equipment. However, downscaling of a disk drive unit that is included in an equipment has long been pursued almost to an extent that structurally a disk can hardly be made smaller any more. Accordingly, further downscaling of a disk drive unit requires a downscaling of components.
Generally, in a disk drive unit of this type, a lead screw is provided on a motor axis of a stepping motor and is engaged with a head carriage to form a drive mechanism. That is, a rotational movement of a stepping motor is converted to a reciprocal movement of a head carriage. The simplest configuration to realize this is the one in which a direction of a movement of a head carriage is parallel with an axis of a stepping motor.
FIG. 1 is a plan view and FIG. 2 is an exploded perspective view of a conventional mechanism for driving a head carriage in a magnetic disk drive unit, as described in Japanese Laid-Open Utility Model Application No. 2-42266. In a body 2 of a stepping motor 1 is provided a stator coil 3, and housed in the stator coil 3 is a cylindrical magnet 4.
A flange provided in the body 2 of the motor, is fixed to a side 13 of a chassis base 12 by a clamp plate 11. This clamp plate 11 fixes the flange between the clamp and the side 13 of the chassis base 12 by tightening a screw 10. In this way the motor 1 is fixed to the chassis base 12, and a motor axis 5 that extends beyond the plane of the flange 9 is housed inside the chassis base 12.
The end of the motor axis 5 is engaged with a bearing 15 fixed to a support post 14 fitted perpendicularly on the bottom of the chassis base 12. The end of the motor axis 5 that resides inside the motor 1 is engaged with a leaf 7 and is pushed permanently by an elastic force toward the direction A shown in the figure. Consequently, the motor axis 5 has no axial play and is kept at the same position permanently. The part of the motor axis 5 that is an extension from the body 2 is threaded in its entirety so that a lead screw 6 is formed.
A head carriage 20 comprising a magnetic head 21 is provided in such a way that it can slip freely along a guide rod 22. The head carriage 20 is provided with a projection 23 which is engaged with the lead screw 6. When the lead screw rotates, the projection 23 gets a propulsion in the axial direction of the lead screw 6, thus making the head carriage 20 to move along the guide rod 22.
A stepping motor is used as the motor 1 and the lead screw 6 is rotated a specified angle at a time. Therefore the head carriage 20 moves in the directions A or B of the figure a specified distance, allowing the magnetic head 21 to move radially over a magnetic disk 24 and to carry out a read/write operation.
When assembling the above mechanism for driving a head carriage, an alignment control is performed whereby the track on the magnetic disk 24 is aligned correctly with the stationary position of the head 21. In this alignment, the motor 1 is rotated on the motor axis 5 so that the stationary position of the head 21 is aligned with a reference track of the disk 24.
On a cap 8, which forms the part of the stepping motor 1 which is opposite from the side the motor axis 5 extends from, is formed a protrusion 25 with a hexagonal shape. In order to perform the above alignment, a jig 26 having a depression that corresponds to the protrusion 25 is employed to rotate the motor 1, so that the alignment of the position of the head 21 and the position of the reference track is determined in a way known in the art. The motor 1 is then fixed to the specified position on the side 13 by tightening the screw 10.
The center of the hexagonally shaped protrusion 25 of the cap 8 is provided with a round inward depression, and is positioned a specified distance away from the part of the leaf 7 which presses the motor axis, when the motor 1 is mounted onto a disk drive unit. When a large force in the direction of B acts on the motor axis at the time of a seek operation on the disk drive, the part of the leaf that produces pressure displaces in the direction of B to a great extent. Since an excess of this displacement fatigues the leaf 7, the round protuberance of the protrusion 25 acts to limit the displacement to a specified amount.
Generally, in a disk drive unit of this type, an overall depth is determined by the size of the disk and the length of the motor for driving a head carriage. Since the protrusion 25 is provided at the back end of the motor 1 to facilitate the engagement to the jig 26, the size of the protrusion 25 makes the motor 1 that much longer at the back end. Accordingly, a disadvantage has arisen in the prior art in that an overall depth of a disk drive unit is made greater due to the size of the protrusion 25, and there has been a demand that an overall depth of a disk drive unit be made smaller.